The Multiprotein Exocyst Complex Is Essential for Cell Separation inSchizosaccharomyces pombe

Abstract

Schizosaccharomyces pombe cells divide by medial fission through the use of an actomyosin-based contractile ring. A mulitlayered division septum is assembled in concert with ring constriction. Finally, cleavage of the inner layer of the division septum results in the liberation of daughter cells. Although numerous studies have focused on actomyosin ring and division septum assembly, little information is available on the mechanism of cell separation. Here we describe a mutant, sec8-1, that is defective in cell separation but not in other aspects of cytokinesis. sec8-1 mutants accumulate about 100-nm vesicles and have reduced secretion of acid phosphatase, suggesting that they are defective in exocytosis. Sec8p is a component of the exocyst complex. Using biochemical methods, we show that Sec8p physically interacts with other members of the exocyst complex, including Sec6p, Sec10p, and Exo70p. These exocyst proteins localize to regions of active exocytosis-at the growing ends of interphase cells and in the medial region of cells undergoing cytokinesis-in an F-actin-dependent and exocytosis-independent manner. Analysis of a number of mutations in various exocyst components has established that these components are essential for cell viability. Interestingly, all exocyst mutants analyzed appear to be able to elongate and to assemble division septa but are defective for cell separation. We therefore propose that the fission yeast exocyst is involved in targeting of enzymes responsible for septum cleavage. We further propose that cell elongation and division septum assembly can continue with minimal levels of exocyst function.

Skp1 and the F-box Protein Pof6 Are Essential for Cell Separation in Fission Yeast

“…It is interesting to note that this subcellular localization is similar to that noted for the Sec8p exocyst component (44).…”

“…ration, a phenomenon that has not been characterized in much detail. However, recently the Sec8 subunit of the exocyst complex was also found to be required for septum processing and cell separation (44), and several other exocyst proteins in addition to Sec8p were found at the septa. Thus it is interesting to speculate that Pof6 and Skp1 functions in cell separation would be related to exocyst function.…”

Evolution of a morphological novelty occurred before genome compaction in a lineage of extreme parasites

“…We speculate that the microsporidian-specific MS channel could be used for spore germination, which involves increased intrasporal osmotic pressure (29). The exocyst complex, which is well known in yeast, functions by the interaction of four subunits-Sec6, Sec8, Sec10, and Exo70-delivering proteins that are essential for cell separation after division (35). Blast searches using the Schizosaccharomyces pombe Sec6 (NP_587736) as query identified a single protein in M. daphniae (OG5_188308; Fig.…”

RalA-exocyst-dependent Recycling Endosome Trafficking Is Required for the Completion of Cytokinesis

“…The Exocyst Is Spatially and Temporally Localized during the Cell Cycle-RalA has been implicated in polarized trafficking through its interaction with the exocyst complex, which plays an essential role in vesicle targeting during cytokinesis in lower organisms (7)(8)(9). We thus postulated that the exocyst complex may also facilitate polarized vesicle trafficking during mammalian cytokinesis.…”

“…Consistent with this notion, the exocyst has been found to concentrate on "hotspots" on the plasma membrane where exocytosis actively takes place and has been implicated in different types of membrane trafficking including polarized growth in yeast, neurite growth in the nervous system, glucose transport in fat cells, and basal-lateral trafficking in epithelial cells (4). Interestingly, in Saccharomyces cerevisiae and Schizosaccharomyces pombe, the exocyst complex localizes to the cleavage furrow and is essential for membrane delivery during cytokinesis (7)(8)(9). However, the role of the exocyst in cytokinesis is poorly understood in mammalian cells, in which the exocyst has a more specialized yet complex function.…”